Machines

ABSTRACT

An unusual kind of wear between machine parts in sliding contact, traceable to environment, is greatly reduced by constituting at least one of the parts of a preferred steel alloy casting consisting essentially of Carbon0.9-1.1Chromium4.0-6.5Molybdenum2.5-7.5Vanadium1.01.75Tungsten2.8 -3.5balance Iron In a specific embodiment, the part is the cam ring of a vane pump obtained by casting the alloy as a centrifugal tube and cutting ring blanks from the end of the tube.

United States Patent [1 1 Adams et a1.

[ Oct. 30, 1973 1 MACHINES [75 Inventors: Cecil E. Adams, Columbus. Ohio;

Joseph J. Connelly, Oakland, N.J.; Joseph F. Krehlik, Columbus, Ohio I73 I Assignee: Abex Corporation, New York, N.Y.

[22] Filed: Nov. 10, 1971 [21] Appl. No: 197,278

Hamaker, Jr 75/126 E 7/1965 Thoma 308/160 8/1940 De Vries 75/126 C Primary Examiner-Charles J. Myhre Assistant ExaminerFrank Susko Attorney-James B. Kinzer et a1.

[57] ABSTRACT An unusual kind of wear between machine parts in sliding contact, traceable to environment, is greatly reduced by constituting at least one of the parts of a preferred steel alloy casting consisting essentially of Carbon ..().9-l.1 Chromium 4.0-6.5 Molybdenum 5-7.5

Vanadium,.. 1.11-1.75 Tungsten 2.8-3.5 balance Iron ln a specific embodiment, the part is the cam ring of a yane pump obtained by casting the alloy as a centrifugal tube and cutting ring blanks from the end of the tube.

21 Claims, 5 Drawing Figures PAIENTEDnmso'mn 3.768.378

' SHEET 2 er 2 F|G.3 I X 33 L f w 40 CUT FlNlSHED I CAM RING 1.... A J l0 HARDEH AND GRIN CENTRIFUGALLY CAST TUSE D TO FIN SH DlMENSIION ornegs 1 MACHINES This invention relates to fluid energy translating devices such as hydraulic pumps, motors, and other machines having parts in sliding contact operating in what is found to be a destructive atmosphere where a lubricating fluid is contaminated with small amounts of moisture and/or soil particles.

A well-known form of heavy duty pump for industrial and mobile equipment purposes is a vane pump. In this kind of pump a rotor is surrounded by a so-called cam ring having a generally eccentric internal diameter (or the rotor could be located eccentrically). The rotor has radial slots at its circumference. The slots support a plurality of blades or vanes with their outer edges in contact with the eccentric part of the cam ring, so that upon rotation of the rotor the vanes are moved in and out relative to the slots in which they are mounted. Oil or other fluid being pumped enters the space between the rotor and ring where the volumetric capacity between adjacent vanes is increasing and is forced out where the volumetric capacity between'the vanes is decreasing. The need for the present invention, the problem, arose in this manner: A small percentage of cam rings in field service were failing to attain life expectancy even under mild operating conditions. Their internal diameter exhibitedeither abnormally heavy ripples (undulations) or large gouges. In contrast, most of the pumps survived without damage, even under severe duty applications. Even though the number of failures was of low order, the problem was great enough to require attention. There seemed to be no explanation for the phenomenon since severe performance and life testing in the laboratory failed to duplicate the condition. No answer was brought forward, in spite of the availability of a sophisticated laboratory facility, until there was recognition of the fact that the pump failures occurred largely when'used with certain fluids in certain geographical areas, a curious aspect which clearly suggested an environment factorf On investigation in the field, oil in the hydraulic system reservoirs was found to be contaminated with small amounts of dirt and water in spite of the fact that the systems were equipped with good filters.

The presence of water and dirt was-a suspect combination along with suspected characteristics of the fluid in use. Soil samples andnew oil of the type being used were collected from local areas where failures had occurred. Back at the laboratory, small amounts of these soil samples .were mixed with water (three-fourths percent to 1 percent) and injected into the perfectly clean oil used in the hydraulic system; under controlled, but mild, test conditions at the laboratory it was found that a rippled or gouged cam ring, typical of the sort of failure experienced in the field, could be developed in about 24 hours with the contaminated pump fluids as thus prepared. The problem was identified, namely, as damage resulting from cooperation of the oil, dirt and water, characteristic of the operating environment, to radically aggravate normal wear. Factors found to influence the amount of wear include variations in fluids used, and the amount and types of contaminants.

The Solution: The environment for failure had been identified, but the cure was something else. There is considerable support for a belief of an electro-chemical corrosion component to the wear, influenced by the make-up and contamination of the hydraulic oils employed, with the electrical energy supplied by streaming current, associated with fluid flow. In recent years, certain aircraft laboratories have made progress on reducing wear damage of hydraulic components, resulting from corrosion driven by streaming currents, by controlling the fluid make up to render it less active electro-chemically. ASME Paper 70-FE-l5 is one publication that discusses this phenomena. However, a pump manufacturer is not in position to dictate, let alone supervise oil use in the field, so he must devise a product to withstand the wear tendency. After nearly three years of effort, our solution, the way to prolong the life of a vane pump cam ring, regardless of the wear modes occurring, in almost any destructive environment encountered, was determined as involving an alteration in metallurgy constituting one aspect of the present invention. While the alteration in metallurgy, hereinafter specified, may appear to be slight, it was not at allapparent during a concentrated three-year study. The alteration is indeed responsible for literally transposing failure into success. Moreover, as we will explain below, our solution is rendered economical and therefore practical in an unusual way, namely, by resorting to a wear resistant material that can be successfully cast into a mold, as well as successfully being cast by a centrifugal process. In other words, we not only developed an alloy as the answer to the problem, we also found an economical way to make cam rings from the alloy. Moreover, and of equal standing, is the fact that this alloy is able to withstand the destructive action of fire resistant fluids, including glycol in water, a fluid with a notorious record for ruining pump parts, including cam rings. Prior to this time, it has been necessary to reduce the operating specifications and warranty period for vane pumps operating on fluids of this type.

The problem and its solution would not be necessarily unique to vane pumps, because the cam ring and vanes of such a pump represent only one example of two parts in severe sliding contact. Thus, the problem could arise in axial piston and gear pumps where there are parts in heavily loaded, sliding contact, and many other kinds of machines as well.

Accordingly, the objects of the present invention are to develop an-alloy to be used as the constituent for the wear resistant face of one of two machine parts in sliding motion, resisting the unusual kind of wear caused by the presence between those parts of a contaminated or destructive fluid, further aggravated by very fine abrasive particles suspended in water and/or oil, and to enable that alloy to be utilized economically for such purposes in spite of its potentially high cost.

Other and further objects of the present invention .will be apparent from the following description and equivalent principles may be used and structural showing a FIG. 3 is an elevation, partly in section, of apparatus employed in producing a centrifugal casting;

FIG. 4 is a fragmentary sectional view, partly in perspective, illustrating the development of a centrifugal casting; and

FIG. 5 is a schematic view showing the preferred mode of practice.

Prior to a detailed description of the present invention, we shall first identify two of the typical pumps representing the most likely forms of the present invention in actual practice. Thus FIG. 1 is a cross section of a vane pump. There are three principal parts, namely, an outer cam ring presenting an internal cam surface 11, more or less elliptical and in any event having an eccentricity in compliance with performance requirements. Located within the cam ring is a rotor 12 provided at its outer circumference'with radially directed slots 13 in which are positioned a like number of hollow blades or vanes 15. The vanes '15 have end edges 16 which, whenthe rotor is rotating, are in sliding contact with the camsurface 11.

The pump illustrated in FIG. 1 is identical to that disclosed in U.S. Letters Pat. No. 3,578,888. We are not here concerned with most of the details of operation, and hence it is sufficient to merely mention that fluid from passages 17 is drawn into suction or inlet zones 18, as the vanes move outwardly, and is pressurized at pressure zones 19 for delivery to exhaust ports 20 as the vanes move inwardly.

However, it should be described briefly that the pump illustrated is of a modern type that employs a basically radially pressure balanced vane with small hydraulic actuators. The actuators urge the vanes against the cam ring with enough force to assure contact, but not with excessive force to produce high stresses or bearing loads at the cam surface.

There are two fundamental types of vane actuator principles in widespread use. The first, and older principle, supplies pump outlet or working pressure to the entire radially inward surface of the vane to thrust the vane against the cam. This principle is illustrated in U. S. Pat. No. 1,989,900, and while quite simple and effective, the force thus supplied is greatly in excess of the requirement, and unnecessarily high vane-to-cam bearing loads and stresses occur.

Pumps of this type are used most often for moderate to light duty as far as pressure is concerned, since the cam would require material that has both good wear resistance and mechanical properties to withstand high pressure operation.

The second, and more modern vane actuating principle employs a vane that is essentially in radial hydraulic balance, with springs or small hydraulic actuating surfaces to deliver enough, but not excessive radial force to the vane to assure contact with the cam.

Examples of pumps of this type are described in U. S. Pats. Nos. 2,856,861 and 2,832,293, and are generallyused for heavy duty or high pressure operation.

In practice, the force thrusting the vane towards the' pared to the second, more modern type. Since the vane-to-cam bearing loads and surface stresses will be different between the two types of pumps, it can be concluded that the mechanical properties desired of the cam surface material in the second type of pumps are not as 'vital as in the first type. This means that some mechanical properties of the cam material could be sacrificed to favor other characteristics, such as wear resistance.

The preferred cast alloy of the present invention, Example 1. below, has exceptionally fine wear resistance entirely adequate for the second more modern type of vane pump in spite of poor mechanical properties such as tensile and elongation compared to wrought alloys; and it possesses similar utility for the first, older type of vane pump except possibly where the thrust force on the vane demands appreciable levels of tensile strength and elongation. As will be shown, there is a family of cast alloys possible, allowing selection.

As explained in detail hereinafter, our invention in its specific or preferred form is concerned with the production of annular parts constituting a cam ring 10. However, the invention could also be applied to an axial piston pump shown in FIG. 2 representing the more complete disclosure in U.S. Letters Pat. 'No. 2,546,583. In this kind of pump, fluid under pressure is developed by pistons 25 operating in chambers 26 presented by a rotating cylinder barrel 27. The ends of the pistons are provided with spherical heads 28 embraced by shoes 29 which engage the sloped surface 30 ofa cam plate 31. When the cylinder barrel 27 is rotating the shoes 29 circumnavigate the cam plate 31 and because of the slope involved the pistons 25 are reciprocated to draw fluid into the piston chambers and then to pressurize it for delivery. The present invention, from its alloy standpoint, could be applied to the pistons 25 or, as will be more likely, the shoes 29 which slide on the cam plate 31. Another part in the piston pump whose life should be extended by use of the material of this invention would be the port plate 32, that is in bearing contact with the rotating cylinder barrel 27.

As suggested, component parts of gear pumps would be expected to have extended life with the material of this invention, as'for example, the gears.

Valve spools, poppets and other parts that sometimes fail by a process sometimes called erosion-corrosion, should also benefit from this material. 7

The standard alloy for vane pump cam rings prevailing for over 20 years has been the one identified as SAE 52,100 in the Metals Handbook (8th Ed.) page 637. This alloy has been supplied in drawn form, that is, it is a worked" alloy, not cast. In fact, steels of this character are most commonly produced as wrought (worked alloys) and seldom, if ever, cast to the best of our knowledge. In any event, the 52,100 alloy was the constituent of the failed cam rings mentioned above. The analysis of SAE 52100 alloy is Mn Si Cr W O.25/0.45 010/035 l.30/l.60 I

with phosphorous and sulfur at 0.025 max.

The extended testing program revealed that a few of While other oil types also produced wear with these contaminants, it was much less severe, and the evidence of the synergism did not exist.

The fluids'in use at the premature job site failures were among the fluids exhibiting this synergism.

It was further'discovered thatall the commercial oils tested containedvarious amounts of water soluble, ionizable, inorganic chemicals. Also, the oils would serve as weak electrolytes, where a galvanic voltage up to 0.5 volt could be read with a sensitive volt meter connected between any two metal pump components of unlike alloy chemistry when submerged in the oil.

Coupled with the streaming current proven to exist in the hydraulic systems during our testing using any of the fluids, all conditions for electro-chemical corrosion existed, and it was interpreted that this corrosion became an influence in the degree of wear experienced.

The streaming current results, in part, by fluid flow relative to the metal walls, and causes an electrical current to flow from the metal wall into the fluid.

It was decided that in such an environment, the soil contamination served to scrub corrosion products from the cam surface, and therefore speed up the process by .continuously exposing fresh metal to the corrosive action.

The magnitude of the voltage and current from the streaming current effect was found to be greater than from the galvanic effect, and increases with flow velocity, and does not exist with no fluid flow. It was decided that ions in the fluid and streaming current could now help explain as erosion-corrosion certain relief valve poppet failures where metal in the high velocity oil flow path was eroded away, sometimes in an area where oil flow at high velocity was diverging from the metal and at other times when it was converging towards the metal.

Since it is not within the scope of a pump and component manufacturer to conduct adequate electrochemical research on all fluids encountered in service, or control their use, it was decided to develop components that could resist wear damage from essentially any cause, including electro-chemical corrosion.

Fluids were then selected that were known toproduce high wear rates on the 52,100 steel with soil and water contamination, which also were suspect to encourage considerable electro-chemical activity, and these were used to evaluate design improvements.

After the prolonged studies culminating in a realization that the answer may reside with metallurgy, the 52,100 alloy was naturally selected as the standard for comparison. An inferior alloy would have a wear rate equal to or worse than 52,100 at an equal cost. A better alloy would show a considerably less wear rate.

Of all the steels tested, only those containing in excess of 2 percent tungsten, vanadium, or the combination of the two, provided enough improvement in wear resistance to be considered.

Of this type, none was available in tubing form as required for cam ring manufacture. This classof steels carry a high base price in keeping with tool steels, and with the added forming charges to convert the solid bars to tubing, the cost was prohibitive.

The search was now aimed at'generating an alloy with a minimum cost of raw alloy materials, a low cost manufacturing means of converting the alloy materials into the tubing form, with the final product having unusual wear resistance for the applications as described.

Included in the qualities desired were satisfactory machinability, ease of grinding, and compatability with mating parts both from a normal wear standpoint and resistance to damage from electro-chemical action. Surprisingly, it was found that a chromiummolybdenum steel alloy having vanadium combined with tungsten in narrow ranges, under stringent allowances for carbon, resulted in an alloy that exhibited as low as 7 percent of the wear rate of 52,100 steel. If tungsten is eliminated, and vanadium increased by what may be termed a partial compensation, for the lack of tungsten, the wear rate is still quite low compared to the standard and is therefore deemed accept able.

EXAMPLE 1 The preferred alloy under the present invention, susceptible to being cast, is as follows:

W P S 2.8/3.5 0.030-Max 0.025 Max Manganese and silicon play no significant role; some silicon is invariably and unavoidably present in a steel, and the balance of silicon together with manganese is used as a deoxidizer in accordance with standard metallurgy practice.

The alloy is cast, and cam rings obtained, as hereinafter described. The finished part,after rough machining, is hardened and tempered as follows: In an atmospherecontrolled furnace (0.9 to 9.0 percent carbon-potential) the cam rings are to be brought up to 760 C, held there for 20 minutes; then raised. to.l,0l0l,038 C and held for a minimum of 30 minutes. The parts are then to be removed from the furnace and quenched in oil (4966 C). The cam rings are then cooled to 49 C and given a double temper at 552580 C for 2 hours, each temper. The part is then finished to size by grinding. i

-A cam ring so produced and carefully tested against one-made of the-52,100 alloy exhibits only about 7 percent of the wear rate of the latter. A cam ring similarly produced, except in compliance with the metallurgy of Example 2 below, exhibits a somewhat higher wear rate compared to the alloy of Example 1, but nonetheless acceptable:

EXAMPLE 2 c Mn Si Cr Mo v 1.07 0.32 0.62 6.4 7.39 3.41 It will be realized from Examples 1 and 2 that most metallurgical experience, we deem an acceptable range for the centrifugally cast part, shown below, particularly as adopted for the cam ring of a vane pump of the second, modern type, to be as follows:

balance substantially all iron except for residual silicon (0.45-0.70) and manganese (0. l 5-0.50) as deoxidizers above is to be imposed on the finished casting.

The present alloy, novel by itself, would nonetheless be classified as a high speed steel on the basis of the chemistry. However, one unusual aspect is that we produce the alloy as a casting, whereas to the best of our knowledge a cast high speed steel has seldom been utilized for anything, at least from the standpoint of commerical production or practice. Such a casting is brittle and cannot be heat treated in a conventional fashion without burning the alloy. This is because segregations in the casting result in a wide range of chemistry within the alloy body and therefore a wide range of melting points. Consequently the high speed steels of commerce employed as cutting tools are hardened by quenching from a temperature in the narrow range of 50 to 100 F displaced below the melting point. A wrought or worked body of the present alloy is entirely unacceptable as too expensive, without providing a wear resistance advantage over the cast material.

In this regard, and now in retrospect, it can be said that the wrought alloy formerly used posseses more mechanical properties than necessary, while having insufficient wear resistance, whereas the alloy of the present invention endows the part with exceptionally fine wear resistance while being poorly endowed with mechanical properties which really are of no value under the circumstances.

Nonetheless we are able to successfully produce cam rings by a centrifugal process as shown in FIGS. 3, 4, and 5. Thus, a heat of the preferred alloy, or within the usable range, is produced and is tapped into a ladle or pouring device 33, FIG. 3, having a pouring spout 34 so constructed and arranged as to project into one end of a circular mold 35 characteristic of a centrifugal mold.

As the charge is poured at a suitable rate into the mold, the latter is rotated, by means not shown. The distribution of molten metal longitudinally of the rotating mold is effected primarily by the action of centrifugal force and the spreading or distribution phenomenon may be visualized from what is shown in FIG. 4 where reference character 37 denotes the stream of molten metal entering the mold from the pouring spout of the ladle, where reference character 38 denotes the progressive wave of molten metal spreading about the internal wall of the centrifugal mold and where reference character 40 denotes the progressively solidifying alloy tube.

There is nothing unusual about a centrifugal casting process. Metallurgists are well versed in this art, but under the present invention we utilize the known technique advantageously to obtain cam rings having an external diameter DA conforming to that of the cam ring shown in FIG. 1 and an internal diameter D8 which can be shaped to the desired contour corresponding to FIG. 1.

Thus the solidified centrifugally cast tube 40, FIG 5, is separated from the mold, annealed and ring blanks 41 are then cut from the end thereof. These ring blanks are rough-machined on the exposed external surfaces and at the internal surface as well, approximately to the finished size, whereafter the temper and hardening treatment set forth above is applied. Finally, the hardened part is ground to the required finished dimension.

In the instance of a solid cam plate such as that used in the axial pump of FIG. 2, or in the instance of another solid part constituted of the present alloy, the solid part may be produced as a static sand casting.

From the standpoint of microstructure heat treated castings embraced by Examples 1 and 2 show a relatively coarse martensitic grain structure with a discontinuous boundary of carbide formations, which include vanadium or tungsten carbides as the case may be.

Although chromium and molybdenum carbides may also be present to some extent, they are not mandatory to provide adequately improved wear resistance.

The chromium and molybdenum tend to impart some useful properties which include some hot strength, and deep hardenability, and allow the part to be heat treated more easily.

However, the chromium and molybdenum are not considered critical.

It is necessary to have enough carbon in the steel casting of the present invention to provide a grain body of Rockwell R,- hardness at least 50 and up to R,-62 (after heat treatment) with residual carbon in sufficient amount to form a vanadium or tungsten (or both) carbide grain boundary network of R hardness at least 70. Examination of additional data withthe foregoing in mind establishes that appreciably reduced wear compared to the 52,100 alloy may be realized by selecting a cast steel alloy within the following broad range, where the alloy may be selected from the standpoint of wear rate, machinability and performance compared to cost:

Cr up to 8 balance iron except for residual amounts of manganese, phosphorous and silicon. In fact, for some special purposes a small amount of nickel may be added or the suggested upper limits on chromium and molybdenum may be exceeded.

The practice of the present invention therefore has several facets, and in its broadest aspect is not necessarily limited to vane-type pumps; it may be applied to other forms of fluid displacement devices, even engines where operation is characterized by one part constantly sweeping another such as the rotor presenting an element in contact with an internal cam surface of a stator.

It will be seen from the foregoing that we faced an unusual problem when encountering a mechanical failure in a very limited number of pump installations which we eventually discovered as possessing a geographic (environment) peculiarity. This in turn led to our discovering that the oil, serviced by the pump and present as a lubricant between opposed parts in sliding contact, was contaminated with a water-in-oil emulsion containing suspended abrasive (earth) particles aggravating normal wear and in fact having something of an exponential influence on wear rate. And while there is some authority to the effect that such wear would be induced by the so-called streaming current phenomenon, our solution was in terms of metallurgy which would present a part resistive to the peculiar type of wear involved and would at the same time slow down the process of the corrosive action which is said to accompany the streaming current effect.

Also while the alloy of the present invention is potentially expensive, and in fact of prohibitive cost if attempted to be drawn, we disclose an inexpensive way to produce rings thereform, by centrifugal casting, and at the same time have an alloy which can be easily produced as a sand casting, that is, simply poured into a static or stationary model of the ordinary kind.

Preferably both opposing parts of'a machine or energy translating device (pump or motor) to which this invention may be applied will be cast from the alloy of the present invention, if cost is justified. For example, both the cam ring and the vanes of a pump could be beneficially constituted of the present alloy. The hardening temperature above specified is suited to the alloy in that hardness is induced at a temperature purposely determined as one which will notburn the. steel, which is to say that we avoidsuperimposing burning or any possible weakening due to segregation;

Hence, while we have disclosed preferred embodiments of the invention it is to be understood that these are capable of variation and modification.

We claim:

1. In a machine where one lubricated metal surface slides on another, producing attrition between the parts which may be-aggravated by undesirable characteristics of the lubricant, the improvement characterized by the wearing face of at least one of said parts being cast of an alloy consisting essentially of Carbon 0.9-1.2 Chromium 4-8 Molybdenum 2-9 Vanadium plus Tungsten 3-6 Balance Iron 2. A' machine according to claim liriwhich the alloy consists essentially of Carbon 0.9-1.2 Chromium 4-8 Molybdenum 2-9 Vanadium 1.0-1.75 Tungsten 2.8-3.5

' Balance lron 3. A machine accordingto claim 1 which is a vane.

Carbon Chromium 4-8 Molybdenum 2-9 Vanadium 1.0-l .75 Tungsten 2.8-3.5

Balance iron 5. A machine according to claim 1 which is an axial piston pump having, a cam plate and a piston member equipped with a shoe sliding on the cam plate member, one of said parts being one of said members.

6. ln a component of a hydraulic system, wherein the component receives and exhausts fluid flow and. includes a part presenting a wear metal surface which is subject to damage by loss of surface material at the fluid-metal interface as fluid flow occurs relative to said metal surface, characterized by said part and its metal surface beingcast from an alloy consisting. essentially Carbon 0.9-1.2 Chromium 4-6 Molybdenum 2-9 Vanadium plus Tungsten 3-6. Balance iron 7. A component accordingto claimfiwherein a sec-- end surface is in bearing contactwith saidfirstmetal surface as said fluid flow is occurring,.the two surfaces having relative movement one to another;

8. A component according to claim 7 embodied in a fluid energy translating device.

9. The fluid energy translating device of claim 8 which is of the vane type.

10. The device of claim 9 wherein the first metal surface is part of a cam that imparts reciprocation'to the vanes of the device.

11. The device of claim 9 wherein said first metal surface is composed of an alloy consisting essentially of Carbon Chromium Molybdenum Vanadium l Tungsten Balance Iron .urge the vanes against the cam surface.

15.The device of claim 14 wherein the alloyconsists essentially of Carbon 0 9 Chromium 4.0- Molybdenum 2 5 Vanadium Tungsten 2.8 Balance lron l6. ln a machine where operation is characterizedby one metal part having a surface sliding on the opposed surface ofanother metal part, improvement comprising one of said surfaces being constituted'ofcast ferrous metal alloy containing about.

Carbon 0.5-1.5 Vanadium plus 2-6 Tungsten Chromium Up to 8 Molybdenum Up to 9 balance substantially all iron, saidl casting beingu'heat treated and characterized by a grain .body hardness of R at least 50 and a carbide grain boundary network. of

R hardness at least 70.

17. A machine according to claim 16 which isa fluid displacement device including acam surface presented by one of said parts, the other of said parts beinga vane.

18. A machine according to claim 16 in twhich the alloy contains about Carbon 0.9-1.2 Vanadium plus .Tungsten 3-6 Chromium 4-8 1 Molybdenum 2-9 19. A machine according to claim l ziin r which the alloy contains about Carbon 0.9-1.2 Vanadium plus Tungsten 3-6 Chromium 4-8 wherein one of the parts is a cam, the improvement Molybdenum characterized by the cam having a wearing surface A mlflchme accordmg to clam 17 whch the formed from a cast alloy consisting essentially of: alloy contains about 5 6.7 .m Ems 042 .2 1

Carbon Chromium Molybdenum Vanadium Tungsten 21. In a vane type fluid energy translating device l0 

2. A machine according to claim 1 in which the alloy consists essentially of Carbon 0.9-1.2 Chromium 4-8 Molybdenum 2-9 Vanadium 1.0-1.75 Tungsten 2.8-3.5 Balance Iron
 3. A machine according to claim 1 which is a vane type fluid energy translating device, one of said parts being the cam of the device.
 4. A device according to claim 3 in which the alloy for the cam consists essentially of Carbon 0.9-1.2 Chromium 4-8 Molybdenum 2-9 Vanadium 1.0-1.75 Tungsten 2.8-3.5 Balance Iron
 5. A machine according to claim 1 which is an axial piston pump having a cam plate and a piston member equipped with a shoe sliding on the cam plate member, one of said parts being one of said members.
 6. In a component of a hydraulic system, wherein the component receives and exhausts fluid flow and includes a part presenting a wear metal surface which is subject to damage by loss of surface material at the fluid-metal interface as fluid flow occurs relative to said metal surface, characterized by said part and its metal surface being cast from an alloy consisting essentially of Carbon 0.9-1.2 Chromium 4-6 Molybdenum 2-9 Vanadium plus Tungsten 3-6 Balance Iron
 7. A component according to claim 6 wherein a second surface is in bearing contact with said first metal surface as said fluid flow is occurring, the two surfaces having relative movement one to another.
 8. A component according to claim 7 embodied in a fluid energy translating device.
 9. The fluid energy translating device of claim 8 which is of the vane type.
 10. The device of claim 9 wherein the first metal surface is part of a cam that imparts reciProcation to the vanes of the device.
 11. The device of claim 9 wherein said first metal surface is composed of an alloy consisting essentially of Carbon 0.9-1.1 Chromium 4.0-6.5 Molybdenum 2.5-7.5 Vanadium 1.0-1.75 Tungsten 2.8-3.5 Balance Iron
 12. The fluid energy translating device of claim 8 which is of the piston type.
 13. The fluid energy translating device of claim 8 which is of the gear type.
 14. The device of claim 10 wherein the vanes are arranged to be largely in radial hydraulic balance with relatively low force vane actuator means provided to urge the vanes against the cam surface.
 15. The device of claim 14 wherein the alloy consists essentially of Carbon 0.9-1.1 Chromium 4.0-6.5 Molybdenum 2.5-7.5 Vanadium 1-1.75 Tungsten 2.8-3.5 Balance Iron
 16. In a machine where operation is characterized by one metal part having a surface sliding on the opposed surface of another metal part, improvement comprising one of said surfaces being constituted of cast ferrous metal alloy containing about Carbon 0.5-1.5 Vanadium plus 2-6 Tungsten Chromium Up to 8 Molybdenum Up to 9 balance substantially all iron, said casting being heat treated and characterized by a grain body hardness of Rc at least 50 and a carbide grain boundary network of Rc hardness at least
 70. 17. A machine according to claim 16 which is a fluid displacement device including a cam surface presented by one of said parts, the other of said parts being a vane.
 18. A machine according to claim 16 in which the alloy contains about Carbon 0.9-1.2 Vanadium plus Tungsten 3-6 Chromium 4-8 Molybdenum 2-9
 19. A machine according to claim 12 in which the alloy contains about Carbon 0.9-1.2 Vanadium plus Tungsten 3-6 Chromium 4-8 Molybdenum 2-9
 20. A machine according to claim 17 in which the alloy contains about Carbon 0.9-1.1 Chromium 4.0-6.5 Molybdenum 2.5-7.5 Vanadium 1.0-1.75 Tungsten 2.8-3.5
 21. In a vane type fluid energy translating device wherein one of the parts is a cam, the improvement characterized by the cam having a wearing surface formed from a cast alloy consisting essentially of: Carbon 0.9-1.1 Chromium 4.0-6.0 Molybdenum 2.5-3.5 Vanadium 1.0-1.75 Tungsten 2.8-3.5 Balance Iron 